Snag tester



July 21, 1954 L. 1. WEINER ETAL SNAG TESTER 2 Sheets-Sheet 1 Filed July 19, 1962 INVENTORS United States Patent 3,141,328 SNAG TESTER Louis I. Weiner, West Newton, and Clarence J. Pope,

Andover, Mass, assignors to the United States of America as represented by the Secretary of the Army Filed July 19, 1962, Ser. No. 211,143 7 Claims. (Cl. 73-159) (Granted under Title 35, US. Code (1952-), sec. 266) The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to an improved method and apparatus for measuring the resistance of fabrics to snag* ging.

Snagging is characterized by a planar deformation of a fabric wherein fibers and/or yarns are lifted up and out of the plane of the fabric. Detailed analyses of snagging produced in actual use in the field and produced in accordance with the present invention indicate that in some fabrics snagging results in a rupturing and pulling out of the yarn structure whereas in other fabrics, e.g., those having high float amplitudes, the floats are pulled up and out of the fabric but are not necessarily ruptured.

The ability of a fabric to resist snagging has been demonstrated to be an indication of the fabrics ability to resist general wear and tear. Fabric durability therefore can be ascertained by determining the ease or difliculty of snagging a sample of the fabric. There has not heretofore been a device that is capable of measuring the tendency of a fabric to snag although there have been devices which measure resistance to tearing or cutting.

It is among the objects of the present invention to pro-. vide a simple reproducible and accurate method of and apparatus for measuring the resistance of fabrics to snagging.

It is also an object of the present invention to provide a snag testing method and apparatus that simulate the type of snagging encountered in actual use of fabrics.

Other objects and advantages of the invention will appear from the following detailed description.

In the accompanying drawings, which form part of this specification, wherein like numerals represent like parts throughout:

FIGURE 1 is a partial side elevational view of an apparatus embodying the invention, a portion of the support and the pendulum being broken away.

FIGURE 2 is a front elevational view, showing the pendulum at the lowermost points of its arc of travel.

FIGURE 3 is a front elevational view of the pendulum.

FIGURE 4 is a fragmentary side elevational view partially in section showing the arc traveled by the needle and the snag in the fabric caused by the needle.

In the drawings, which for purpose of illustration, depict one embodiment of the present invention, the numeral designates the base of the apparatus supported by three legs 11 with adjustable foot portions 12. The base 10 supports a frame which comprises spaced upstanding arms 13, disposed adjacent the sides of the base and intermediate the front and rear ends thereof. A cross piece 14 connects the top of the arms and forms the top of the frame.

The specimen supporting platform comprises a hollow rectangular box-like material support 15 having a fiat and smooth upper surface 16. The support 15 extends from a point spaced a substantial distance in front of frame arms 13 to a point spaced behind the rear portions of the frame arms. Platform side plates 17 are arranged at each .side of the material support 15 and are secured thereto by bolts or the like. The side plates 17 extend a substantial distance beyond the rear edge of the support 15 to a point 3,141,328 Patented July 21, 1964 spaced beyond the rear edge of base 10. A roller 18 is mounted on a transverse roller shaft 19 connecting the rear portions of side plates 17. The roller is mounted for free rotation and has its upper surface arranged in the plane of the flat upper surface 16. The rear portion of the roller extends a short distance beyond the rearmost portions of the side plates 17 The specimen supporting platform is mounted upon a pedestal 20 which in turn is mounted upon the base 10 between the spaced arms 13.

A vise bracket 21 is attached to the forward face of the support 15 and has an upstanding flange 22 extending in spaced parallel relation to the forward face of the support 15 to provide a recess between the forward face of the support 15 and the upright flange 22. A pair of clamping or vise screws 23 extend through the flange and into the recess and are threadably engaged in the flange. The vise screws are adapted to engage the front section of a piece of specimen fabric 24 and to hold it firmly in position against the forward face of the support 15.

A fabric strip 24 thus engaged is drawn over and lies in contact with the flat upper surface 16 of the specimen supporting platform and extends over the roller 18 where it is engaged by a spring clamp 25. A weight 26 is suspended from the spring clamp 25 by means of a hook 27. The specimen fabric 24 is tautly drawn across the upper surface 16 of the support 15 by the weight 26. The weight may be varied to vary the tension of the fabric.

A cross shaft 30 is journaled for rotation in suitable anti-friction bearings located in cars 31 protruding from the forward edge of the frame arms 13 at a point spaced below the top of the arms. A pendulum arm 32 is rigidly secured at 33 to the cross shaft 30 to rotate therewith and is provided with a head comprising a U-shaped frame 34 secured to the pendulum and having a cross piece 35 connecting the two ends of the frame 34. A pair of depending guide arms 36 are attached to the sides of frame 34 and span the specimen supporting platform.

As shown in detail in FIGURE 3 there is mounted in the head of the pendulum and more specifically in the crosspiece 35 thereof a micrometer 37 disposed axially of the pendulum arm 32. A micrometer, the details of construction and operation of which are well known to those skilled in the art, is an instrument that is finely adjustable by means of screw threads and is capable of measuring very small distances. As shown in the drawings, the micrometer comprises a thirnble 40 that may b manually rotated to cause it to advance along a barrel having a scale marked thereon that measures the distance traveled by a spindle 38 that is movable along the axis of the micrometer. The spindle may be moved away from or towards the crosspiece depending on the direction of rotation of the thimble.

Aflixed to the lower end of the spindle 38 is a pointed snagging element 39. As seen in FIGURE 4, the snagging element initially extends downwardly axially of the spindle 38 and at about its midpoint it is bent at an angle of approximately The end of the snagging element 39 is positioned so as to point in the direction of and lie in the plane of travel of the pendulum arm 32 and in this position is capable of contacting the surface of the fabric 24 at an angle varying from about 80 to about from a plane perpendicular to the plane of the fabric.

menses 3 permit clockwise rotation of the pendulum as viewed in FIGURES 1 and 4 but prevent the counterclockwise return of the pendulum until the ratchet pawl is released.

The crosspiece 14 connecting the top of arms 13 supports a forwardly projecting housing shelf 44. The forward end of the housing shelf is beveled as best seen in FIGURE 1. A latch pin .45 extends upwardly through an opening in the beveled face of the housing shelf 44 projecting a short distance thereabove to engage a notch in bracket 46 clamped to the pendulum arm 32 as illustrated in FIGURE 1 where the pendulum arm is shown in its raised and latched position. The head of a plunger 47 extends through an opening in the top of the housing. When the head of the plunger is depressed it moves an arm (not shown) acting against a spring (not shown) to withdraw the latch pin 45 from the bracket notch and release the pendulum arm 32. When the pendulum is again raised the bracket 46 will ride over the latch pin depressing it and the pin will then be raised by the spring to engage the bracket notch.

In operation, the fabric specimen 24 to be tested is secured by vise screws 23 at one end and is then drawn over the fiat upper surface 16 of the support and over the roller 19 where the opposite end is gripped by clamp 25 with weight 26 attached. The specimen is held in a smooth taut condition over the flat upper surface 16. The pendulum is manually lowered and the snagging element 39 is positioned by adjusting the micrometer 37 so that the snagging element Will just clear the fabric surface. The pendulum is raised to its upper position where it is held by the latch pin.

Plunger 47 is depressed releasing the pendulum arm 32 and the snagging element describes an are over and beyond the fabric 24 until the force of its momentum is expended. At this point pawl 43 engages one of the teeth of ratchet wheel 41 and retains the pendulum arm 32 in this position until the pawl is released. The pendulum is reset to its upper position where it is held by the latch pin. The micrometer is adjusted so as to lower the snagging element 39 by .001 inch and the pendulum again released. Downward adjustments of the snagging element are repeated until the are described by the snagging element produces a visible snag 49 in the surface of the fabric specimen. The precision and reproducibility of this test is evidenced by the fact that raising the snagging element by .001 inch above the setting required to produce the first visible snag will permit an arc or swing of the pendulum that will leave the fabric intact whereas lowering the snagging element by .001 inch from the setting that produced the first visible snag will result in a cutting or tearing of the yarns of the fabric.

The end point of the test occurs when the investigator observes the first visual evidence of snagging in the fabric structure. The depth of penetration of the snagging needle into the surface of the fabric structure required to produce the snag is a measure of the snagging tendency of the fabric. The point of the snagging element is calibrated with reference to the upper surface 16 of the support 15. The thickness of the test fabric is determined under a pressure of 0.625 p.s.i. since at this pressure high amplitude floats, i.e., yarn loops that stand well above the fabric structure, and loose fibers can be pressed into the fabric structure.

The height of the snagging point above the upper surface 16 that produces a snag in the fabric is determined by reading off the micrometer scale. From this value is substracted the theoretical thickness of the test fabric. The resulting value is a measured of the depth of penetration of the needle into the theoretical position of the fabric surface and is an indication of the tendency of the fabric to snag. For example, a combed twill fabric (8.2 oz.) has been observed to snag at a point .005 inch above the theoretical position of the fabric surface as established by thickness measurement at 0.625 p.s.i. which indicatS a poor resistance to snagging. The depth of penetration of the snagging element into a 9.0 oz. Oxford fabric to produce a snag occurs at .003 inch below the theoretical position of the fabric surface which is indicative of a high resistance to snagging.

The greater the distance above the theoretical position of the fabric surface to the point at which a snag is first observed, the greater the tendency to snag, and the greater the distance below the theoretical fabric surface to the point at which a snag is first observed the less the tendency of the fabric to snag.

The method and apparatus described herein for measuring snag resistance of fabrics possess the advantages of simulating the type of snagging encountered in the field use of textile fabrics, of being more reproducible than other textile measuring devices since the basis of measurement employed herein is a length unit that is measurable in terms of .001 inch, of not having to require the use of complicated force measuring systems, and of not having to require a separation of the energy required to snag from that required to cut or tear.

While one embodiment of the invention has been shown for purposes of illustration, it is to be understood that various changes in the size, shape and arrangement of parts may be resorted to without departing from the spirit or scope of the invention as expressed in the appended claims.

We claim:

1. The method of measuring the resistance of fabric material to snagging which comprises the steps of:

(a) placing a strip of fabric material in a plane parallel to and spaced from a plane tangent to the arc of a freely swinging needle, said needle positioned at an angle of approximately with respect to the radius of said are and pointed in the same direction as the path of said arc,

(b) increasing the radius of said are by a measured amount with each swing until the needle snags the fabric,

(0) measuring the depth of penetration of the snagging needle into the surface of the fabric structure necessary to produce a snag, which measurement is a function of the snag resistance of the fabric.

2. The method of measuring the resistance of a fabric material to snagging which comprises the steps of (a) securing a strip of fabric material over a support,

(b) swinging a weighted needle in an are over the surface of said fabric material, the radius of said arc traveling in a plane perpendicular to the plane of said fabric material, said needle set at an angle of approximately 90 with respect to the radius of said arc and directed along the path of said arc,

(c) increasing the radius of said are by a measured amount with each swing until the needle snags said fabric material,

(d) measuring the depth of penetration of the snagging needle into the surface of the fabric structure necessary to produce a snag, which measurement is a function of the snag resistance of the fabric.

3. The method of measuring the resistance of fabric material to snagging which comprises the steps of:

(a) securing a strip of fabric material over a support,

(b) swinging a needle fixed to the end of a pendulum in an are over the surface of said fabric material, said pendulum arm traveling in a plane perpendicular to the plane of said fabric material, said needle set at an angle of approximately 90 with respect to the pendulum arm and directed along the path of said arc,

(0) increasing the radius of said arc by a measured amount with each swing until the needle snags said fabric material,

(d) determining the depth of penetration of the snagging needle into the surface of the fabric structure necessary to produce a snag by measuring the distance between the top surface of said fabric and the point at which said snag occurs, which distance is a function of the snag resistance of the fabric.

4. The method of measuring the resistance of fabric material to snagging which comprises the steps of:

(a) securing a strip of fabric material over a flat support,

(b) swinging a needle in an are over the surface of said fabric material, said needle extending axially from the end of a pendulum arm that swings through a plane perpendicular to the plane of the fabric, said needle bent at an angle of approximately 90 so as to point along the path of the are,

(c) adjusting the needle axially of the pendulum arm so as to increase the radius of the arc of the needle with each swing until the needle snags the fabric material,

(d) determining the depth of penetration of the needle into the fabric structure necessary to produce a snag by measuring the distance between the theoretical top surface of said fabric and the point at which said snag occurs, which distance is a function of the snag resistance of the fabric.

5. In a snag testing apparatus, a supporting frame, a pendulum pivotally supported by said frame, a needle secured to the end of said pendulum at an angle of approximately 90 thereto and pointed in the same direction as that traveled by said pendulum, a material support carried by said frame below the pendulum pivot and in a plane perpendicular to the plane of travel of the pendulum, means carried by said pendulum to vary the radius of the are described by the pendulum needle by a measured amount.

6. In a snag testing apparatus, a supporting frame, a pendulum pivotally supported by said frame, a snagging needle secured to the end of said pendulum at an angle of approximately thereto and pointed in the direction of the plane of travel of said pendulum, a material support carried by said frame below the pendulum pivot in a plane spaced from and perpendicular to the plane of travel of the pendulum, means carried by said pendulum to vary the radius of the are described by the pendulum needle by a measured amount.

7. In a snag testing apparatus, a supporting frame, a pendulum pivotally supported by said frame, a snagging needle secured to the end of said pendulum extending axially thereof and bent at an angle of approximately 90 With the tip of said needle pointed in the direction of the plane of travel of said pendulum, a fixed material support carried by said frame below the pendulum pivot in a plane spaced from and perpendicular to the plane of travel of the pendulum, means carried by said pendulum to vary the radius of the are described by the pendulum needle by a measured amount.

Boor Apr. 26, 1955 Thomas July 17, 1962 

6. IN A SNAG TESTING APPARATUS, A SUPPORTING FRAME, A PENDULUM PIVOTALLY SUPPORTED BY SAID FRAME, A SNAGGING NEEDLE SECURED TO THE END OF SAID PENDULUM AT AN ANGLE OF APPROXIMATELY 90* THERETO AND POINTED IN THE DIRECTION OF THE PLANE OF TRAVEL OF SAID PENDULUM, A MATERIAL SUPPORT CARRIED BY SAID FRAME BELOW THE PENDULUM PIVOT IN A PLANE SPACED FROM AND PERPENDICULAR TO THE PLANE OF TRAVEL OF THE PENDULUM, MEANS CARRIED BY SAID PENDULUM TO VARY THE RADIUS OF THE ARC DESCRIBED BY THE PENDULUM NEEDLE BY A MEASURED AMOUNT. 